Thermal efficiency and engine-out emissions from an internal combustion engine are determined by many factors including the combustion system design and the mechanical design. Combustion system design includes combustion chamber shape, the fuel injection nozzle, and the fuel injection pressure, intake manifold and exhaust manifold, etc. All of these together are optimized to achieve mixing quality that leads to effective combustion.
An unconventional engine that is being developed to exploit its high power density and other positive characteristics is an opposed-piston engine. Conventional direct-injection diesel combustion chamber geometry does not work for the opposed-piston engine because the centrally-located injector in conventional engines is not feasible in an opposed-piston engine because the combustion chamber is contained between two piston faces. In the opposed piston engine, the only position in which a conventional injector can be installed to have access to the combustion chamber is in the cylinder wall. It has been found that a toroidally-shaped combustion chamber provides a very favorable combustion characteristic. It would be desirable to obtain such desirable combustion and emission characteristics in other engine architectures.